This invention relates to electrical switches and more particularly to a compact non-contact capacitance switch for on/off or on/off/dimmer control of an electrical circuit.
Most household or office electrical circuits, particularly those related to lighting, typically utilize mechanical switches. These mechanical switches may be of the contact type for on/off activation, or include a means for varying the power supplied to the circuit, i.e., to perform a xe2x80x9cdimmingxe2x80x9d function, to variably alter power supplied to a light or to act as a speed control for a fan.
Non-contact switches that rely on a change in capacitance to perform an on/off function have been proposed. These devices sense the presence or absence of an object in front of the switch by the change in capacitance.
In U.S. Pat. No. 5,973,6081, a non-contact switching system is described that utilizes selected components to provide on/off and dimming functions. However, the components in one embodiment are preferably housed at a centralized location, requiring dedicated wring from the sensors to the central controller and then back to the activated circuits.
In addition, the dimming function is achieved in defined steps which require particular components for each step, further increasing costs and complexity. For example, the ""608 patent uses outputs of a capacitive sensor at predetermined levels to activate different stepped levels of dimmer output. This means that the number of capacitive sensor outputs is proportional to possible dimmer levels. A digital value representing those levels is passed through a programmable logic device (PLD) and then latched. Latch output determines output power level. This means that the number of power control outputs is proportional to the output power levels. To construct a smooth dimmer, small increments in output power level are needed, which requires a proportionally high number of power control outputs, and thus multiple large components with a high number of pin counts (PLD, latch, clock chips). Even if a CPU were considered for use in the device, the input pin count would still be equal to the sensor output number and the output pin count equal to the latch output number of the CPU, which would still be proportional to the number of stepped dimmer levels, requiring a large CPU chip and numerous interconnections and peripheral components in the circuit.
Control of the ""608 switch is hand movement dependent. To switch the light on, the band must be moved from the furthest zone into the closest zone of the sensor. To switch the light off, the hand must be pulled from the closest zone into the furthest zone of the sensor. Clearly two different types of movement are needed for basic operation of the switch. To users unfamiliar with the device this could result in confusion.
In U.S. Pat. No. 5,716,129, a non-contact switch includes an oscillator having a frequency output that varies with proximity of a hand. The components are intended for insertion into a lamp base or an ornamental shell. The component count and/or component size are quite large and would not fit into a standard wall box, as is clear from the view showing these components in a lamp base, and this is without a dimmer control circuit. The device is clearly not capable of functioning as a direct replacement of a mechanical wall mounted switch. The device also requires both a neutral and a live connection to the AC power source, while in many wallboxes and circuit designs, only one lead is accessible, rendering such a device useless as a direct replacement.
A particular problem with the prior art is the inability to provide a direct replacement for a mechanical switch. For example, a direct replacement of a mechanical on/off toggle switch must be capable of fitting within a space defined by a common electrical box. Utilizing special size boxes or special wiring adds substantially to the cost of installation, and is prohibitive in any retrofit application.
It is an object of the present invention to provide a non-contact proximity type switch for controlling an electrical circuit.
It is a further object to provide a non-contact capacitance electrical switch that has a compact integral construction, only requiring connection to conventional wire leads for mounting in new or existing wall boxes.
It is yet another object of the present invention to provide an integral compact non-contact electrical switch that has a minimum number of components to reduce costs and improve reliability.
These and other objects of the present invention are achieved by a non-contact electrical switch for use in an electrical circuit for controlling an electrical device comprising:
a capacitance sensor;
means for detecting an AC period zero crossing;
a central processing unit (CPU) connected to the capacitance sensor and having means for receiving a signal therefrom, and for processing the signal to generate an output signal, and having signal processing means for receiving the output signal and calculating a power output in response thereto relative to the AC period zero crossing, and for generating a control signal used for controlling power in the electrical circuit.
In one embodiment, the output signal may generate a triac firing pulse, a delay between the AC period zero crossing and the firing pulse determining the quantity of power delivered to the circuit.
Preferably, the non-contact electrical switch includes an interference detector which generates a signal that is received by the CPU to avoid inadvertent activation and/or to zero out electromagnetic and line interference, for example caused by lightning, faulty electrical appliances, etc.
The inventive switch uses a capacitance sensor to control a power supply to the electrical circuit. The capacitance sensor detects the presence of an object in front of the switch, turning the power on/off or performing a dimming function. The sensor reacts to the change of capacitance, caused by the change of dielectric constant of the medium in front of the sensor. The switch only reacts on a capacitance change rather than on fixed capacitance values. Advantages of such a design over prior non-contact switches such as capacitance, infra-red, sound, light sensor, movement to detector etc. are:
1) Switch control is independent of the front plate material, color, shape etc., as there is no need to conduct a physical contact control signal via a conductive element (for example as with a touch plate sensor).
2) There are no accommodations necessary to accept mechanical limitations to the front plate design as there are no moving parts, unlike mechanical toggle switches and mechanically controlled dimmers.
3) The capacitance sensor can penetrate through various materials, so there is no need for an opening in the front plate for the sensor to operate, unlike infra-red or various sound, light, and motion sensors.
4) The front plates are freely interchangeable since the switch is capable of recalibrating to each new material fixed in front of it.
5) The switch is immune to dirt or grime on the front plate, unlike touch plate sensors, IR and other optical sensors, since any amount of dirt is treated by the capacitance sensor as a fixed object and calibrated out.
6) The switch can be completely sealed since it doesn""t incorporate any mechanical moving parts, unlike mechanical switches and mechanically controlled dimmers, which also increases reliability.
7) The operation of the switch is completely spark-free.
A wide range of front plate designs from simple plastic to artistic ceramic could be used with the switch. All natural materials such as stone, crystal, wood etc. or other materials such as plastics, glass, ceramics, rubber etc. could be used for the front plate. There are virtually no limitations except as to maximum combined weight. The switch can be used with various front plate designs purely for decorative or aesthetic reasons, but it could also be used when physical contact with a switch is not desired, for example, when operating a switch in a hospital, public lavatories etc. or where the environment contains dust, dirt etc that may accumulate on the front plate. Since the switch can be sealed, it can also be used in harsh environmental conditions such as when exposed to the elements, to mist or fumes etc., and thus it is applicable to outdoor and/or industrial uses.
The switch can directly replace a standard household wall switch. That is, it can be fitted into an existing wallbox of standard dimensions and be connected to the existing wiring, allowing direct retrofitting in existing electrical circuits. The switch can be connected either in series (i.e. a two-wire connection) as a direct replacement of a regular wall switch where only a single lead is accessible, or in parallel (i.e. a three-wire connection) if the load requires such connection and the wires are accessible in the wallbox. The switch can be provided as a full range smoothly operated dimmer control as well as an on/off switch.
The switch can readily be designed to meet all international standards. Because it is of compact integral construction, substantial space remains in the wallbox beyond that needed by the switch itself, so there is enough room left in the wallbox for wiring. In addition, a metal cooling surface or other heat sink can be incorporated into the switch so as to comply with various heat dissipation standards.
Another advantage of the present invention is that it does not use absolute predetermined values of capacitance to control the switch. With the ""608 Patent device, to turn the switch fully on, the hand has to come into the closest zone to the sensor. Since this zone is fixed, it could be inside the wall, for example if the sensor is mounted too deeply into a wall recess or if the sensor is covered by a cover plate that is too thick. In both cases it would be impossible to turn the switch fully on since the closest sensor zone would be inaccessible. A similar problem could occur if a permanent conductive object were mounted near the ""608 sensor. This surface would distort the electrical field of the sensor resulting in reduced sensor sensitivity, as zones become closer to the sensor surface. Both problems could possibly be overcome by setting the sensor parameters manually or automatically. If the sensor parameters are adjusted manually, each user of the switch would be responsible for these settings, which is a significant drawback since this would complicate installation. For automatic sensor adjustment, special circuitry must be added to the sensor since the ""608 device is not capable of auto-calibration, increasing component count and overall device size and complexity.
In the inventive switch, this problem is solved by reacting on the capacitance change rather than on the absolute value. The flag for detecting the presence of an object is set when capacitance in front of the sensor is increased. There is no fixed predetermined level at which presence is detected. By this the switch is also self-calibrated, as it cancels out any permanent capacitance changes in front of the sensor. This auto-calibration may be implemented completely in software without any increase in component count or in the size of the inventive switch.
The present invention operates independent of hand speed and no special moves are necessary in front of the sensor to activate the basic function of the switch. It always changes the state if the hand is put near the sensor.